Adding a class to each menu item in the primary links

Today I wanted to add a unique identifier to each menu item in the primary links so I could theme each one individually. In this example, I added a incrementing class to each menu item so I could add an image via css. Here's a snippet of my theme function (found in template.php):

<?php
function MYTHEME_preprocess_page(&$variables) {
  $linkCount = 0;
  foreach ($variables['primary_links'] as $k => $v) {
    $linkCount++;
    $class = trim($v['attributes']['class'] . " nav$linkCount");
    $variables['primary_links'][$k]['attributes']['class'] .= $class; 
  }
}
?>